William the Conqueror, the Duke of Normandy, invaded and conquered England and the Anglo-Saxons in 1066 AD. (The Bayeux Tapestry, details of which form the navigation buttons on this site, is perhaps the most famous graphical depiction of the Norman Conquest.) The new overlords spoke a dialect of Old French known as Anglo-Norman. The Normans were also of Germanic stock ("Norman" comes from "Norseman") and Anglo-Norman was a French dialect that had considerable Germanic influences in addition to the basic Latin roots.

Prior to the Norman Conquest, Latin had been only a minor influence on the English language, mainly through vestiges of the Roman occupation and from the conversion of Britain to Christianity in the seventh century (ecclesiastical terms such as priest, vicar, and mass came into the language this way), but now there was a wholesale infusion of Romance (Anglo-Norman) words.

The influence of the Normans can be illustrated by looking at two words, beef and cow. Beef, commonly eaten by the aristocracy, derives from the Anglo-Norman, while the Anglo-Saxon commoners, who tended the cattle, retained the Germanic cow. Many legal terms, such as indict, jury, and verdict have Anglo-Norman roots because the Normans ran the courts. This split, where words commonly used by the aristocracy have Romantic roots and words frequently used by the Anglo-Saxon commoners have Germanic roots, can be seen in many instances.

Sometimes French words replaced Old English words; crime replaced firen and uncle replaced eam. Other times, French and Old English components combined to form a new word, as the French gentle and the Germanic man formed gentleman. Other times, two different words with roughly the same meaning survive into modern English. Thus we have the Germanic doom and the French judgment, or wish and desire.

It is useful to compare various versions of a familiar text to see the differences between Old, Middle, and Modern English.

In 1204 AD, King John lost the province of Normandy to the King of France. This began a process where the Norman nobles of England became increasingly estranged from their French cousins. England became the chief concern of the nobility, rather than their estates in France, and consequently the nobility adopted a modified English as their native tongue. About 150 years later, the Black Death (1349-50) killed about one third of the English population. The laboring and merchant classes grew in economic and social importance, and along with them English increased in importance compared to Anglo-Norman.

This mixture of the two languages came to be known as Middle English. The most famous example of Middle English is Chaucer's Canterbury Tales. Unlike Old English, Middle English can be read, albeit with difficulty, by modern English-speaking people.

By 1362, the linguistic division between the nobility and the commoners was largely over. In that year, the Statute of Pleading was adopted, which made English the language of the courts and it began to be used in Parliament.The Middle English period came to a close around 1500 AD with the rise of Modern English.